Reland of "Mustash: Ensure surfaces submitted to Mus by WM and embedders contain Surfaces with embe…

services/ui/ws/platform_display_delegate.h

Index: services/ui/ws/platform_display_delegate.h
diff --git a/services/ui/ws/platform_display_delegate.h b/services/ui/ws/platform_display_delegate.h
index 0358573ffcfa7cdbb2dda4cc0ad503fdb0ce0eec..808717bb57439d2bd0d105f8dfb46dade8cbb89c 100644
--- a/services/ui/ws/platform_display_delegate.h
+++ b/services/ui/ws/platform_display_delegate.h
@@ -28,6 +28,9 @@ class PlatformDisplayDelegate {
   // Returns the root window of this display.
   virtual ServerWindow* GetRootWindow() = 0;
 
+  // Returns the root window of the active user.
+  virtual ServerWindow* GetActiveRootWindow() = 0;
+
   // Called once when the AcceleratedWidget is available for drawing.
   virtual void OnAcceleratedWidgetAvailable() = 0;